Authorities in Brazil are investigating whether vigilantes seeking revenge for the deaths of two police officers were behind a bloody night of killings that left at least 19 dead in greater São Paulo late Thursday, refocusing attention on Brazil’s history of police violence.

In one incident, captured in a chilling two-minute video, shooters in ski-masks and windbreakers entered a bar on a western outskirt, selected several patrons, calmly lined them up against a wall and shot them, leaving eight dead.

Minutes later, a similar shooting nearby left two more dead, authorities said. All told, shootings took place at eight locations in about two hours.